Blade of the Blood Mage

Weapon Simple, Cursed, Light Rare (this item requires attunement)

A curved dagger with a red hilt, the blade seemingly covered in a dark, viscous liquid that can't seem to be wiped away. When held, the wielder's arm goes cold and numb, seeming to draw the warmth and energy down into the blade. As a bonus action, you can spend up to half of your HP and add that number to your damage roll. If you miss, the extra damage will halve each turn until it reaches 0 or you manage to hit the target. When unattuned, the blade leaves the wielder's arm numb long after the battle is over. Until a long or short rest, take a -2 to any DEX or STR check that requires use of your arms. Take a -4 DEX or STR penalty for any check that relies on just that arm (Wielding any other one handed weapon, for example.)